The 4-month-old Gray Seal was discovered by families strolling along the beach in Babylon.
Park officials contacted the Riverhead Foundation for Marine Research and Preservation.
Foundation supervisor Julika Wocial told Newsday that it removed the seal because it appeared to have a jaw injury. An examination confirmed that the jaw was broken and infected. The seal is being treated with antibiotics.
Wocial said the seal will remain at the foundation for several weeks.